The activated sludge process has been used for many years for the removal of both biological (or alternatively biochemical) oxygen demand (BOD) and ammoniacal nitrogen values from wastewater. The BOD which is usually expressed as BOD.sub.5, generally, and in the present invention, refers to the oxidation of organic carbon compounds by heterotropic microorganisms. The oxidation of ammoniacal nitrogen values is effected by autotrophic microorganisms which derive their energy for growth by oxidation of ammoniacal nitrogen values to NOX. The energy so produced is then utilized to produce protein material from inorganic components such as water, carbon dioxide and ammonia.
It is known that both the BOD and ammoniacal nitrogen values can be removed from wastewater in a single sludge system, the latter being removed by oxidation of ammonia to NOX. In those cases in which denitrification is required, the NOX may be reduced to volatile nitrogen compounds such as N.sub.2 O or N.sub.2. Alternatively, a substantial volume of NOX-containing wastewater may be recycled to an anoxic zone within a wastewater treatment system such as that described in FIG. 2 of U.S. Pat. No. 4,056,465 and one form of that which is described by J. Barnard, Water and Waste Engineering (1974) 33, and the subject of South African Pat. No. 725371.
In systems of this type, the NOX is reduced, to form N.sub.2 for example, by serving as an electron receptor for sorbed organisms. In these cases, the oxidizing power of the NOX is utilized for the oxidation of organic carbon compounds. All biological wastewater processes which are capable of effective nitrification must provide for longer sludge ages relative to the sludge age for systems which require removal of BOD alone. The minimum sludge age for nitrification systems of this type varies from about one-and-a-half days at 30.degree. C. to about 10 days at 10.degree. C.
The removal of ammoniacal nitrogen values is important for those systems in which the oxygen demand of ammonia degrades the quality of the receiving stream by removing oxygen values. The total removal of nitrogen values, including both ammonia and NOX is important when the element nitrogen is harmful in that it causes excessive growth of flora and/or algae in receiving streams.